1. Field of the Invention
The present invention is related to electron beam controlled bulk semiconductor switches and, more particularly, to a switch which is not restricted by the space charge limited current condition and is capable of high current gain and high current density.
2. Description of the Related Art
Many varieties of optically controlled semiconductor switches exist, but electron beam controlled switches are less common. Photodiodes, phototransistors, photothyristors and light sensitive resistors are examples of the many types of optically controlled switches. The most commonly used light-sensitive semiconductor deice is the photodiode which is used in many applications, including fiber optic communication systems, etc. The currents handled by such devices are relatively low, typically in the milliampere range. One example is the PIN diode taught by U.S. Pat. No. 4,240,088 to Myers. Other light-activated devices include the thyristors taught by U.S. Pat. Nos. 3,832,732 to Roberts and 4,001,865 to Voss, the microwave switching circuit taught by U.S. Pat. No. 4,396,833 to Pan and many other patents. Some, such as U.S. Pat. No. 4,626,883 to Kash et al. and 3,917,943 to Auston, describe switching elements with picosecond switching times. Other light activated switches, such as those taught by U.S. Pat. No. 4,438,331 to Davis and 4,376,285 to Leonberqer et al., are able to carry a larger amount of current by making an entire block of semiconductor material conductive; however, like photodiodes, they require continuous light to sustain conduction.
Electron-bombarded semiconductor (EBS) devices are high-speed switching devices which use an electron beam instead of light to control switching. EBS devices typically use electron beams of 10-15 keV and are limited in output power and current density due to the space charge limited current condition. While switching time is typically below ten nanoseconds, the current density is usually a few milliamperes per square millimeter with a current gain of 2000 or less.
Higher current densities, up to 1O.sup.2 A/cmz.sup.2 are provided by diffuse discharge switches, such as the switch taught by U.S. Pat. No. 4,0643,130 to Hunter. However, while diffuse discharge switches can be turned ON in less than a nanosecond, they are relatively slow to turn OFF, taking approximately 100 nanoseconds and have a moderate current gain between 10.sup.2 and 10.sup.3.